In a toroidal type continuously variable transmission for a vehicle, speed control has been performed using oil pressure, as indicated for example in Tokkai Hei 6-257661 published by the Japanese Patent Office in 1994. This continuously variable transmission is a so-called double cavity type transmission in which two sets of toroidal gearing units are arranged parallel to each other. One unit possesses a pair of power rollers 18c and 18d inside a casing 10 as shown in FIG. 9. The power rollers 18c and 18d are supported by a pair of trunnions 4a, 4b via eccentric axes 6a, 6b such that they are free to rotate.
The power rollers 18c and 18d are gripped by the input disk and the output disk which are not shown in the drawing, and an arbitrary speed change is achieved by varying a gyration angle around the Z axis according to a displacement in the Z axis direction shown in the figure of the trunnions 4a and 4b.
The trunnion 4a is driven in the Z axis direction via a trunnion axis 5A by an oil pressure servo-cylinder 1, and the trunnion 4b is driven in the Z axis direction by an oil pressure servo-cylinder 1B.
The oil pressure servo-cylinder 1A comprises a piston 31 joined to the trunnion axis 5A.
The piston 31 is displaced together with the trunnion axis 5A in the Z axis direction according to a differential pressure of upper and lower oil chambers 33L, 33H. The trunnion axis 5A rotates together with the trunnion 4a around the Z axis according to gyrational displacements of the power roller 18c.
The oil pressure servo-cylinder 1B is operated in the same way as the oil pressure servo-cylinder 1A by the piston 32, and oil chambers 34L, 34H.
A hydraulic fluid is supplied through a control valve 41 to each of the above-mentioned oil chambers. The control valve 41 is housed inside an oil pan 10A joined to the lower part of the casing 10.
The control valve 41 comprises a spool 43 which is displaced by a step motor 50 in the X axis direction of the figure. The spool 43 is inserted inside a shaft sleeve 42, either of the oil chambers 33L, 33H or 34L, 34H being connected to an oil pressure pump and either of the oil chambers 33L, 33H, or 34L, 34H being connected to a drain according to the relative displacement of the spool 43 and shaft sleeve 42. In this way, the power rollers 18c and 18d are always displaced in the up/down direction of the figure centered on the rotation axis 17 of input/output disks.
The lower end of the trunnion axis 5A supporting the power roller 18c projects inside the oil pan 10A. At the lower end of this trunnion axis 5A, a precess cam 2 having a guide groove 21 inclined at a predetermined angle is installed. The precess cam 2 converts the rotational displacement of the trunnion axis 5A around the Z axis into a displacement in the Z axis direction, and transmits this to an L type link 99. The L type link 99 is joined to the shaft sleeve 42, so the displacement in the Z axis direction is converted into a displacement in the X axis direction which is transmitted to the sleeve 42. In this way, the gyration angle of the power roller 18c is fed back to the control valve 41.
The other toroidal speed change unit of the continuously variable transmission has an input axis 17 and output axis which are common with the aforesaid unit, and it varies the gyration angle under oil pressure control based on the feedback of the common control valve 41 and gyration angle of the power roller 18c.
In this continuously variable transmission, the control valve 41 is installed between the two speed change units when viewed from the Z axis direction of FIG. 9. This is due to the fact that the four trunnion axes project inside the oil pan 10A in order that these trunnion axes do not interfere with the control valve 41. The step motor 50 is arranged so that its rotation axis is parallel to the Z axis as shown in FIG. 9, and it drives the spool 43 via a rack-and-pinion gear 98.
However, this arrangement of the step motor 50 is a factor in increasing the depth of oil pan 10A. If the rotation axis of the step motor 50 is arranged to be parallel to a plane containing the X axis and Y axis when the rotation axis 17 of the transmission is the Y axis, the oil pan 10A need not to be deepened, but in such an arrangement of the step motor 50, the motor interferes with the trunnion axis as described above, which is undesirable.
Also, to increase the speed change rate of the transmission, the capacity of the step motor must be large, but the capacity increase of the step motor increases the dimensions of the transmission in the Z axis direction, i.e. the up/down direction, and this results in a smaller clearance between the oil pan and the ground.
In this context, Tokkai Hei 7-198015 published by the Japanese Patent Office in 1995, discloses a continuously variable transmission which has a step motor and a spool valve arranged horizontally in parallel with each other.
This arrangement was enabled by connecting the rotation axis of the step motor and the spool of the spool valve via a link and a screw mechanism.
However, even in this case, there is still a possibility that the horizontally arranged step motor interferes with a strainer disposed in the oil pan.